1. Field of the Invention
The present invention relates generally to a multi-band antenna, and more particularly to a Ultra Wide Band antenna (UWB) used for electronic devices, such as notebooks.
2. Description of the Prior Art
At present, the Bluetooth and the IEEE802.11a/g are two of main wire network technologies. However, both the two wire network technologies have disadvantage that transmitting rate of signals fall down with the increase of transmitting distance. A new technology, Ultra Wide Band (UWB) interknit technology, is used in short-haul signal high-speed transmission and signal low-speed transmission among over 100 m even to 1 km distance. The system in electronic device sends low-intensity and narrow pulse signal but not carrier signal to achieve high quality and high-speed transfer. For this reason, this signal transmission has strong anti-jamming capability, and smaller loss of power and electric. Besides, UWB has a big advantage of big capacity to transmit more data. In Feb. 14, 2002, FCC in USA allowed UWB interknit technology used on consumer electrical products. To achieve Ultra Wide Band transmission, an UWB antenna is designed. The band width of the antenna lies on the impedance matching degree, so the UWB antennas need higher requirement of impedance. In current technique, most of UWB antennas are monopole antennas or dipole antennas. However, present electric devices require small-size, so smaller antenna therein is needed. Plane inverted F antennas, a kind of antennas with small size, are used more and more. U.S. Pat. No. 7,042,414 discloses an UWB antenna with small size as shown by FIG. 1 with label of this patent. The antenna comprises two different radiating elements working on two bands having across frequency band to achieve Ultra Wide band. The first radiating element 31 of the antenna is a plate with a cutout in the middle of itself, and the second radiating element 32 is made by a kind of material different from that of the first radiating element. The second radiating element 32 is located in the cutout of the first radiating element 31, and separated from the first radiating element 31. The UWB antenna has better radiation properties, but the radiating elements of the antenna and the grounding element are divided into two parts which are not connected with each other. So the radiating elements and the grounding element must be fastened through a PCB, thus, the structure of the antenna is complex. U.S. Pat. No. 5,828,340 discloses a wide band antenna as shown by its FIG. 1 with label. The wide band antenna comprises a plate 10 with a cone shape angle 20 and being located on the substrate 4, a grounding element 14 and a feeding line 12. The wide band antenna 2 is able to achieve frequencies lower or higher than the center frequency 40%. However, the radiating element of the wide band antenna is made of an integral planar plate 10 resulted in the volume of the antenna is big.
Hence, an improved antenna is desired to overcome the above-mentioned shortcomings of the existing antennas.